1. Field of the Invention
This invention relates to electrical switching apparatus and, more particularly, to that class of such apparatus which is actuatable automatically in response to fluid pressures or pressure differentials applied thereto.
Still more specifically, this invention is concerned with providing an improved organization and constructions for such apparatus to enhance the performance and versatility of application thereof, while also reducing the size, cost and complexity thereof.
2. Description of the Prior Art
In the most general sense, the essential primary elements of, say, a normally open, single pole, electrical switch are well known and would include a pair of electrically conductive contacts, some means typically of electrically insulative material for supporting the contacts in normally spaced relationship to each other, and some means for permitting and causing at least one of the contacts to move into engagement with the other for effecting an electrical connection therewith. It is also known that the contacts themselves may be rigid with the supporting means therefor permitting one to be moved toward the other or at least one of the contacts may be formed of resilient material permitting it to be temporarily deformed so that a portion of same will engage the other contact; that the means for supporting the contacts may be either yieldable or rigid to cooperate with the nature of the contacts; that auxiliary mechanisms such as springs may be employed to bias one or both of the contacts toward their normal separated juxtaposition; and that various means may be utilized for actuating one contact into engagement with the other, including by the application of manual force to one or both contacts (typically through some yieldable, electrically insulative cover or handle to electrically isolate the person applying such force from the contacts themselves), by the application of machine generated mechanical forces to one or both contacts (typically through some appropriate auxiliary linkage or interengagement of parts), by the application of magnetic forces (typically through some form of armature associated with one of the contacts), or by the application of fluid pressure produced forces (typically through movement of a diaphragm or piston mechanically linked or shiftable into interengagement with one of the contacts).
Within such framework of known fundamentals, a great diversity of electrical switching devices have been proposed or constructed having widely differing constructional and operational characteristics and intended for utilization in a variety of applications and environments, although none are known that achieve the significant combination of advantages provided by the improved organization and constructions of the present invention.
Although probably not directly relevant to the present invention, the general state of the prior art respecting electrical switching devices intended and adapted for use in applications in which actuation of the switch is responsive to a manually applied pressing or squeezing force, either directly or through some intermediate instrumentality such as driving a vehicle over a treadle, are illustrated by the following U.S. Patents: Armstrong U.S. Pat. No. 2,244,933, Schwinn U.S. Pat. No. 2,367,441, Burke U.S. Pat. No. 2,583,813, Schulenburg U.S. Pat. No. 2,823,279, Cooper U.S. Pat. No. 2,909,628, Hohmann U.S. Pat. No. 2,959,647, Mahoney U.S. Pat. No. 2,975,350, and Weissburg U.S. Pat. No. 3,209,089. Similarly, the state of the prior art respecting electrical switching devices that are responsive to fluid pressure, but wherein a diaphragm or other element that is shifted in response to fluid pressure is opposed by some mechanical biasing means such as a spring or by magnetic means is illustrated by the following U.S. Patents: Muerle U.S. Pat. No. 2,412,095, Kennelly U.S. Pat. No. 2,439,474, McGee U.S. Pat. No. 3,038,044, Gold U.S. Pat. No. 3,300,703 and Kolze U.S. Pat. No. 3,366,760. Another approach to accomplishing an electrical switching function in response to an extreme fluid pressure condition sufficient to destroy a rupture disc or the like and thereby mechanically free a biasing element to permit or cause switch closure is illustrated by the Lewis U.S. Pat. No. 2,230,961.
Of greater specific interest as background for the present invention, however, would seem to be the state of the prior art with respect to electrical switching devices that respond more directly to a fluid pressure differential, which is illustrated in terms of differentials between positive fluid pressure levels, differentials between a positive fluid pressure level and a vacuum, etc., by the following U.S. Patents: Bast U.S. Pat. No. 1,684,530, Lupold et al. U.S. Pat. No. 1,974,779, Wesley et al. U.S. Pat. No. 2,251,180, Garland U.S. Pat. No. 2,253,425, Hard af Segerstad U.S. Pat. No. 2,421,149, Gill U.S. Pat. No. 2,505,539, Winter U.S. Pat. No. 2,561,962, Edwards, Jr., et al. U.S. Pat. No. 2,919,320, Lindberg, Jr., U.S. Pat. No. 3,180,956 and Basile et al. U.S. Pat. No. 3,267,233. Although the construction and arrangement of parts involved in the devices of the last mentioned group of prior patentees are diverse and the disclosures of such patents reveal various intended specific applications for such devices, it is believed fair to observe both that such patents seem to indicate a general trend toward increasing complexity with time and constructional approaches characterized by relatively large size and attendant costs of initial manufacture and replacement. Moreover, none of such prior devices found to have been disclosed in the apparently more pertinent area of the prior art appear well suited for versatile utilization in diverse applications, including those reqiring satisfaction of a combination of stringent operating characteristics such as physical miniaturization, quick response time, sensitivity to relatively low levels of change in fluid pressures, or reliable operation in adverse environments involving corrosive fluids or unusually high or low temperatures.
It is believed, therefore, that the previously existing state of the prior art relating to fluid pressure responsive electrical switching apparatus has left unfulfilled a long standing and important need for improvements in the organization and construction of the noted class of devices to overcome the mentioned disadvantages and limitations of what has heretofore been available.